Hollow Cages versus Space-Filling Structures for Medium-Sized Gold Clusters:  The Spherical Aromaticity of the Au₅₀ Cage

Abstract

Candidates for the lowest energy structures of medium-sized Au(n), n = 32, 38, 44, 50, and 56, clusters were evaluated using gradient-corrected DFT computations. Both hollow cage and space-filling conformations were considered. The cages were constructed using fullerene-based templates. The space-filling structures were generated by employing a genetic algorithm. We have found that the space-filling isomers were lower in energy except for two notable cases. Like Au(32) [Johansson, M. P.; Sundholm, D.; Vaara, J. Angew. Chem. Int. Ed. 2004, 43, 2678], a hollow cage configuration of Au(50) is more stable than its alternative space-filling isomeric forms. The unusual stabilities of the cage Au(32) and Au(50) can be attributed to spherical aromaticity; both exhibit large negative nucleus-independent chemical shifts and exceptionally large HOMO-LUMO gaps.

Planar and cagelike structures of gold clusters: Density-functional pseudopotential calculations

“…This consideration points again to the importance of good exchange-correlation functionals in dealing with the DFT structural description of gold clusters. 16,17 . On the other hand, although all atoms of Au 20 are at the surface, this cluster can be considered as a small piece of bulk fcc gold 4,12,13 .…”

Evidence of hollow golden cages

“…However, photoelectron spectroscopy (PES) combined with theoretical calculations shows that at the relatively large size the overwhelming population of low-lying clusters for Au 32 Ϫ near room temperature appears to consist of only compact structures because of the entropic factor (7). Other, larger gold clusters with cage-like local minimum structures also have been suggested (8,9), but none has been observed experimentally. Conversely, it has been established from both ion-mobility (10) and PES (11) experiments that the most stable anion gold clusters (Au n Ϫ ) in the size range n ϭ 5-13 possess planar structures and that a structural transition from planar to three-dimensional (3D) structures occurs at n ϭ 14.…”

A first principles density functional investigation of ligand-protected eight atom gold nanoclusters

“…Several experimental and theoretical studies have predicted this number to fall in a range from 6 to 13. [8][9][10][11][12][13][14][15][16][17][18][19][20] For anionic and cationic gold clusters the 2D-3D transitions are observed to occur at N = 13 and N = 8, respectively. Theoretical calculations for neutral clusters have predicted the transition to occur at six, 8 seven, 9, 10 eight 11,12 as well as in the range from 11-15 atom clusters.…”

“…Theoretical calculations for neutral clusters have predicted the transition to occur at six, 8 seven, 9, 10 eight 11,12 as well as in the range from 11-15 atom clusters. [13][14][15][16][17][18][19][20] It has been anticipated that the different methods and models adopted to determine the cluster size at which the 2D-3D transition takes place can possibly be one of the reasons for the large spread in the obtained results (from [6][7][8][9][10][11][12][13][14][15]. Gold clusters are reported to retain their planar structures to cluster sizes larger compared to Ag and Cu clusters which remain planar upto 7 atom cluster sizes only.…”